The formation of polar nanoregions through solid-solution additions is known to enhance significantly the functional properties of ferroelectric materials. Despite considerable progress in ...characterizing the microscopic behavior of polar nanoregions (PNR), understanding their real-space atomic structure and dynamics of their formation remains a considerable challenge. Here, using the method of dynamic pair distribution function, we provide direct insights into the role of solid-solution additions towards the stabilization of polar nanoregions in the Pb-free ferroelectric of Ba(Zr,Ti)O_{3}. It is shown that for an optimum level of substitution of Ti by larger Zr ions, the dynamics of atomic displacements for ferroelectric polarization are slowed sufficiently below THz frequencies, which leads to increased local correlation among dipoles within PNRs. The dynamic pair distribution function technique demonstrates a unique capability to obtain insights into locally correlated atomic dynamics in disordered materials, including new Pb-free ferroelectrics, which is necessary to understand and control their functional properties.
Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants in consumer goods, such as plastics, electronics, textiles, and construction material. PBDEs have been found in human milk, ...fat, and blood samples. Rodent studies indicate that PBDEs may be detrimental to neuro-development, possibly by lowering thyroid hormone concentrations in blood. In the present study, we determined concentrations of PBDEs and thyroid hormones in human fetal and maternal serum. Patients presenting in labor to Indiana University and Wishard Memorial County hospitals in Indianapolis, who were older than 18 years, were recruited to participate. Twelve paired samples of maternal and cord blood were obtained and analyzed using gas chromatographic mass spectrometry; thyroid hormone concentrations were determined by radioimmunoassay. Six congeners of PBDE were measured in maternal and fetal serum samples. The concentrations of total PBDEs found in maternal sera ranged from 15 to 580 ng/g lipid, and the concentrations found in fetal samples ranged from 14 to 460 ng/g lipid. Individual fetal blood concentrations did not differ from the corresponding maternal concentrations, indicating that measurement of maternal PBDE blood levels is useful in predicting fetal exposure; similarly, other reports have shown a high correlation between PBDE in mother's milk and fetal exposure. In accord with reports on other biologic samples, the tetrabrominated PBDE congener BDE-47 accounted for 53-64% of total PBDEs in the serum. The concentrations of PBDEs found in maternal and fetal serum samples were 20-106-fold higher than the levels reported previously in a similar population of Swedish mothers and infants. In this small sample, there was no apparent correlation between serum PBDEs and thyroid hormone concentrations. Our study shows that human fetuses in the United States may be exposed to relatively high levels of PBDEs. Further investigation is required to determine if these levels are specific to central Indiana and to assess the toxic potential of these exposure levels.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Reducing thermal noise from optical coatings is crucial to reaching the required sensitivity in next generation interferometric gravitational-waves detectors. Here we show that adding TiO$_2$ to ...Ta$_2$O$_5$ in Ta$_2$O$_5$/SiO$_2$ coatings reduces the internal friction and in addition present data confirming it reduces thermal noise. We also show that TiO$_2$-doped Ta$_2$O$_5$/SiO$_2$ coatings are close to satisfying the optical absorption requirements of second generation gravitational-wave detectors.
Recent results on achieving ferromagnetism in transition-metal-doped GaN, AlN and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carriers ...in new generations of transistors, lasers and integrated magnetic sensors. There is strong potential for new classes of ultra-low-power, high-speed memory, logic and photonic devices based on spintronics. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures and most theories predict that the Curie temperature will be a strong function of bandgap. We discuss the current state-of-the-art in producing room temperature ferromagnetism in GaN-based materials, the origins of the magnetism and its potential applications.
Around the globe several observatories are seeking the first direct detection of gravitational waves (GWs). These waves are predicted by Einstein's general theory of relativity and are generated, for ...example, by black-hole binary systems. Present GW detectors are Michelson-type kilometre-scale laser interferometers measuring the distance changes between mirrors suspended in vacuum. The sensitivity of these detectors at frequencies above several hundred hertz is limited by the vacuum (zero-point) fluctuations of the electromagnetic field. A quantum technology--the injection of squeezed light--offers a solution to this problem. Here we demonstrate the squeezed-light enhancement of GEO 600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3-4 years. GEO 600 now operates with its best ever sensitivity, which proves the usefulness of quantum entanglement and the qualification of squeezed light as a key technology for future GW astronomy.
ABSTRACT
We present spectra of Eris from the MMT 6.5 m Telescope and Red Channel Spectrograph (5700–9800 Å, 5 Å pixel
−1
) on Mt. Hopkins, AZ, and of Pluto from the Steward Observatory 2.3 m ...Telescope and Boller and Chivens Spectrograph (7100–9400 Å, 2 Å pixel
−1
) on Kitt Peak, AZ. In addition, we present laboratory transmission spectra of methane–nitrogen and methane–argon ice mixtures. By anchoring our analysis in methane and nitrogen solubilities in one another as expressed in the phase diagram of Prokhvatilov & Yantsevich, and comparing methane bands in our Eris and Pluto spectra and methane bands in our laboratory spectra of methane and nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are ∼10% and ∼90% and Pluto's bulk methane and nitrogen abundances are ∼3% and ∼97%. Such abundances for Pluto are consistent with values reported in the literature. It appears that the bulk volatile composition of Eris is similar to the bulk volatile composition of Pluto. Both objects appear to be dominated by nitrogen ice. Our analysis also suggests, unlike previous work reported in the literature, that the methane and nitrogen stoichiometry is constant with depth into the surface of Eris. Finally, we point out that our Eris spectrum is also consistent with a laboratory ice mixture consisting of 40% methane and 60% argon. Although we cannot rule out an argon-rich surface, it seems more likely that nitrogen is the dominant species on Eris because the nitrogen ice 2.15 μm band is seen in spectra of Pluto and Triton.
We present an up-to-date, comprehensive summary of the rates for all types of compact binary coalescence sources detectable by the Initial and Advanced versions of the ground-based gravitational-wave ...detectors LIGO and Virgo. Astrophysical estimates for compact-binary coalescence rates depend on a number of assumptions and unknown model parameters, and are still uncertain. The most confident among these estimates are the rate predictions for coalescing binary neutron stars which are based on extrapolations from observed binary pulsars in our Galaxy. These yield a likely coalescence rate of 100 per Myr per Milky Way Equivalent Galaxy (MWEG), although the rate could plausibly range from 1 per Myr per MWEG to 1000 per Myr per MWEG. We convert coalescence rates into detection rates based on data from the LIGO S5 and Virgo VSR2 science runs and projected sensitivities for our Advanced detectors. Using the detector sensitivities derived from these data, we find a likely detection rate of 0.02 per year for Initial LIGO-Virgo interferometers, with a plausible range between 0.0002 and 0.2 per year. The likely binary neutron-star detection rate for the Advanced LIGO-Virgo network increases to 40 events per year, with a range between 0.4 and 400 per year.
Low mechanical loss, high index-of-refraction thin-film coating materials are of particular interest to the gravitational wave detection community, where reduced mirror coating thermal noise in ...gravitational wave detectors is desirable. Current studies are focused on understanding the loss of amorphous metal oxides such as SiO sub(2), Ta sub(2)O sub(5) and HfO sub(2). Here, we report recent measurements of the temperature dependence of the mechanical loss of ion-beam sputtered hafnium dioxide (HfO sub(2)) coatings that have undergone heat treatment. The results indicate that, even when partially crystallized, these coatings have lower loss than amorphous Ta sub(2)O sub(5) films below ~100 K and that their loss exhibits some features which are heat-treatment dependent in the temperature range of ~100?200 K, with higher heat treatment yielding lower mechanical loss. The potential for using silica doping of hafnia coatings to prevent crystallization is discussed.
Some proposed interferometric gravitational wave detectors of the next generation are designed to use silicon test masses cooled to cryogenic temperatures. The test masses will need to be partially ...coated with high emissivity coating to provide sufficient cooling when they absorb the laser light. The mechanical loss of the Acktar Black coating is determined based on the measurements of the Q-factors of the bending vibration modes of coated and uncoated commercial silicon wafers. The Young's modulus of the coating material is determined using nanoindentation. We use this information to calculate thermal noise of the silicon test masses associated with a high emissivity coating on its lateral side (barrel). It is found that such a coating results in a less than 9% increase of the total strain noise of LIGO Voyager design for a future cryogenic gravitational wave detector.
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